1. Field of the Invention
This invention generally relates to color printer and digital imaging technology and, more particularly, to a method for calibrating a printer three-dimensional signal space into perceptually uniform gradations.
2. Description of the Related Art
Every color printer or color imaging system operates by defining a color space. Although different systems exist for defining color, one common system is the three dimensional signal space forming a cube with a black (O) vertex, a white (W) vertex, the three primary color vertices; red (R), green (G), and blue (B), and three secondary vertices; cyan (C), magenta (M), and yellow (Y). This color space is known as RGB or CMY. Other definitions of color space, such as CMYK, can be translated into the above-described system.
However, the color space definitions between different printers need not necessarily be the same. Alternately stated, a pixel with a specific color space definition does not necessarily appear the same when printed from different printers. For example, an imaging software application loaded on a personal computer (PC) may intend to create a pixel defined as 10% red, 10% green, and 80% blue (10, 10, 80). This pixel information is sent to two different color printers associated with the PC. When printed on the first printer, the pixel may appear as (10, 10, 80), as intended. However, due to variances between manufactures, for example, the pixel at the second printer may actually appear as (10, 15, 75) on the first printer when objectively measured. Alternately stated, the color instructions sent by the PC are device dependent. In this circumstance, a perfect match between intended and actual pixel colors can only occur if RGB color space profile of both printers can be derived, and a conversion invented to translate between the PC color space and the printer color space.
In generating color conversion tables for printers, there is a need to extensively sample the device color space (such as RGB, CMY, or CMYK) to create a printer target. It is highly desirable to sample the device color space in such a way that the output colors are more or less evenly distributed in a perceptual uniform color space, such as the CIELAB space. However, different types of printers have different characteristics and it is not possible to have one target that works equally well for all types of printers.
It would be advantageous if a printer's color, or signal space could be calibrated to create a perceptually uniform color space.
It would be advantageous if a printer's color space profile could be easily generated, to permit the printer to render perceptually consistent colors.